(NewsNation) — The death of Riley Strain, a University of Missouri student who went missing in Nashville, Tennessee, for nearly two weeks, appears to be accidental, police say, but his parents still have questions.

Strain’s parents have ordered a second autopsy despite the preliminary autopsy that determined his death to be “accidental.”

Police announced last week that Strain had been found dead in the Cumberland River about 8 miles west of downtown and foul play was not suspected.

Police previously said Strain, 22, was last seen just before 10 p.m. on March 8 after drinking downtown. University of Missouri officials said in a statement that Strain was traveling to Nashville to attend a private event.

Despite authorities saying there was no foul play involved, some details of the preliminary report are raising questions among his family members. The complete autopsy and toxicology report could take weeks or even months to be released.

“One thing that threw the family for a loop was the coroner going on record stating about the lack of water in his lungs,” Strain’s family friend told NewsNation. “Usually water in the lungs means that they were alive when they went into the water.”

The police report also stated that Strain was only found with his watch and shirt, and was just half dressed from the waist down.

Forensic analyst Joseph Scott Morgan joined “Elizabeth Vargas Reports” on Thursday to weigh in, saying further investigation is needed.

“Anytime that we have someone that is unclad, particularly in the lower body, it’s rather provocative when you begin to think about and so we take a harder look at those kinds of cases because any number of things can at least be implied we have to follow that line of logic to its finality,” Morgan said.

As to why there was no water found in his lungs, forensic expert Dr. Michelle Dupre told NewsNation it doesn’t necessarily mean he didn’t drown.

Dupre explained that there are two ways to drown: wet drowning, when you ingest water, and dry drowning, when you have a laryngospasm. In dry drowning, the body reacts to water entering the system by automatically closing up the airways, which means neither water nor oxygen is getting into the lungs.

Strain’s family awaits the results of the final autopsy, hoping to get some answers about Riley’s final moments.